As described in the electrical engineers' journal "Denki Kyodo Kenkyu" (Electrical Joint Research), volume 41, No. 5, page 67-68 and in the Japanese Utility Model Laid-Open No. 80616/1981, it is known that measures taken in substations to improve reliability of power systems include duplication of the main bus; sectionalizing the bus to make the sectioned buses individually operational and to provide a bus section unit to connect the sectioned buses; and providing a bus tie unit to connect parallel double buses and connecting feeder units between the double buses.
The above substation configuration is explained by referring to FIG. 1 which is a one-line diagram of the substation circuitry. The main bus 2 and the main buses 1 and 3 constitute a double bus scheme in which two parallel main buses are laid. The main buses 1 and 3, which together form one of the two parallel buses, are arranged in line on the same axis and are disconnectably connected with each other by a bus section unit S. The bus section unit S consists of a disconnecting switch 4b connected at one end to the main bus 1, another disconnecting switch 4a connected at one end to the main bus 3, and a circuit breaker 5 connected between these disconnecting switches. The parallel main buses 1 and 2 or buses 2 and 3 are connected by a bus tie unit T in such a way as to be disconnectable so that power can be interchanged between these buses. A feeder unit F is disconnectably connected between the main buses 1 and 2 or between the buses 2 and 3 to supply transformers and loads.
In the above configuration, for inspection or during failure of the main bus 3 which is connected to the main bus 1 through the bus section unit S, the circuit breaker 5 is operated, the disconnecting switches 4a, 4b are opened, and the bus tie section T is also operated so as to leave the remaining main buses 1 and 2 operational.
For application in substations with the above configuration, the Japanese Utility Model Laid-Open No. 80616/1981 shows the bus section unit S which is formed by a gas-insulated switchgear. In this example, two separated gas-insulated main buses arranged in line on the same axis on the installation area are connected by an auxiliary gas-insulated jointing bus which is located by the side of the opposing ends of the two aligned gas-insulated main buses. The gas-insulated main buses and the auxiliary gas-insulated jointing bus need be arranged parallelly. This increases the widthwise dimension, which in turn increases the installation area of the gas-insulated switchgear used as the bus section unit.